Method and apparatus for chemical vapor deposition capable of preventing contamination and enhancing film growth rate

ABSTRACT

Disclosed relates to a method for CVD comprises steps of injecting a purge gas, which doesn&#39;t either dissolve or generate byproducts by itself, into a reaction chamber where substrates are located; and supplying a source material of vapor phase participating directly in forming a film on the substrates to an inside of the reaction chamber, thus forming a protective curtain in the inside of the reaction chamber by a mutual diffusion-suppressing action between the purge gas and source material. Besides, the invention provides an apparatus for CVD including a susceptor located in a reaction chamber producing a vacuum, on which substrates are placed and a film deposition process is made, the apparatus comprising: a reactive gas confining means, established over the susceptor, having at least a source material supply port through which a source material is supplied and a plurality of openings perforated on a surface thereof; a purge gas supply port through which a purge gas is fed into an outside of the reactive gas confining means; and an exhaust port for discharging exhaust gasses generated in the reaction chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a method and apparatus forchemical vapor deposition (CVD), and more particularly to a method andapparatus for CVD that prevents contamination and enhancing film growthrate by directing a reactive gas for forming a film to the midst of areaction chamber, and concentrating the reactive gas diffused over asusceptor in the chamber to prevent the reactive gas from being touchingcomponents of the reaction chamber.

2. Description of the Related Art

Chemical vapor deposition (CVD) is a thin film deposition process forforming solid material over the surface of a substrate using a reactant(usually in the form of gas, i.e., a reactive gas). As depicted in FIG.1, a conventional apparatus for CVD comprises in general a reactionchamber 3 producing a vacuum, an inlet 7 for supplying the reactive gasto the chamber 3, a heating means 44 for chemically reacting thereactive gas supplied, outlets 6 for discharging exhaust gas, and asusceptor 5, located in the midst of the chamber 3, on which a substrate55 is placed and the deposition occurs. When a given composition ofvapor phase, including a main source material that participates directlyin forming films and an auxiliary source material for carrying,vaporizing or diluting the main source material, is injected into thevacuum chamber 3, the composition is diffused instantly in alldirections, such that the density of the reactive gas may have finitevalue at all over the inside of the reaction chamber. Especially, aportion of the composition in the vicinity of the susceptor is excitedby hot temperature of the susceptor to form films on the substrate.

The conventional CVD apparatus is mainly used for making thin films lessthan 3 μm in thickness due to a low growth rate. To form a thick filmmore than 3 μm in thickness, it is necessary to increase the density ofthe reactive gas in the chamber considerably. However, the reactive gasinjected into the chamber 3 generates undesired films or powders on thereaction chamber components such as walls, reactive gas distributingshowerheads, substrate heating devices, inspection windows, etc.Moreover, the undesired films and/or powders formed on the reactionchamber components are broken to be small particles by repeated thermalexpansion/contraction and/or lattice parameter mismatch between thereaction chamber components, thus contaminating the thin films whilemanufacturing. Here, if the number of the contaminant particles in thechamber 3 is increased, the reliability of the manufacturing process isdeteriorated seriously. For example, in case of making very large scaleintegration (VLSI), the contaminant particles result in serious patterninferiority such as circuit short.

Meanwhile, to enhance film growth rates in the conventional CVD system,it is necessary to increase the density of the reactive gas in thevicinity of the susceptor by adding the reactive gas to all space of thechamber 3 in practice, which requires the amount of the reactive gasexcessively, thus deteriorating the economic efficiency.

To prevent contamination and undesired deposits in the reaction chamber3, it may be considered to regulate the chamber temperatureappropriately. However, the range of the temperature regulatable is verynarrow, and furthermore, if the reactive gas is composed of severalsource materials, the range of temperature to regulate doesn't existactually. Consequently, it is impossible to prevent generation ofcontaminant particles by regulating the reaction chamber temperature.

Besides, in the conventional CVD system, the temperature differencebetween the inner wall of the chamber 3 and the susceptor 5 causes anatural convection, which makes it difficult to maintain the diffusionof the reactive gas uniformly onto the substrates, thus deterioratingthe reliability of the films formed. Moreover, the natural convectionmakes the contaminant particles generated continue to re-circulate inthe chamber, which aggravates the problem of the contamination.

Accordingly, to manufacture a thick film more than 3 μm in thickness orVLSI circuits rapidly and economically, it is required to provide animproved method and apparatus for CVD that can prevent contamination,even when highly concentrated reactive gas is injected into the reactionchamber, and increase the density of the reactive gas in the vicinity ofthe susceptor in the reaction chamber considerably without raising theamount of the reactive gas supplied.

Following two conventional methods relate to the methods for increasingthe density of the reactive gas in the vicinity of the susceptor in thechamber 3, and preventing generation of contaminant particles,respectively, which are considered as prior arts of the presentinvention.

First, as depicted in FIG. 2, U.S. Pat. No. 5,851,589 describes a CVDapparatus including a first gas, containing a reactive gas, fed inparallel to the surface of the substrate 55 through a pipe 2, and asecond gas, containing a purge gas (non-reactive-gas), blownperpendicularly towards the surface of the substrate 55 through ainjecting plate 1 to stabilize and make laminar flowing state of thefirst gas. Next, referring to FIG. 3, U.S. Pat. No. 6,301,434 disclosesa dual gas manifold providing purge gas through a top showerhead 6 toprevent deposits on the window 8 and providing reactive gas through alower showerhead 7 to deposit films on the substrate 55. The prior artsdescribed above positively employed the control of purge gas to relaxthe conventional contamination problem. However, it seems thatrelaxation of the contamination is done only at the limited portion ofthe whole reaction chamber in both prior arts cited.

In FIG. 2, there exists an unavoidable re-circulation zone near theleading edge of the substrate, and it is difficult to suppress thediffusion of the reactive gas to the chamber wall, which deterioratesthe effectiveness of the reference system. Moreover, the externalcontrol of purge gas flow rate may need much trial to make the reactivegas flow stabilized, since the laminar flow zone of the reactive gas isvery narrow while the purge gas suppresses the narrow zone overallperpendicularly, thereby involving the latent instability of the flow.In FIG. 3, although the purge gas control system may be effective inpreventing deposits on the window of the lamp system, it is not surewhether the reference apparatus could prevent particles being formed onthe surface of the reaction chamber components such as chamber walls,especially around the areas far away from the purge gas showerhead. Thisproblem would become serious when long process time and/or high growthrate is required.

Accordingly, the present invention is invented to provide a method andapparatus for chemical vapor deposition, which eliminates the drawbacksof the above-mentioned prior art. That is, the method and apparatus forCVD can form efficiently thick films more than 3 μm in thickness of highquality with excellent reproducibility, uniformity, controllability, andhigh growth rate using a protective curtain formed by a mutualdiffusion-suppressing action between the purge gas and reactive gas.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for CVD comprising steps of injecting a purge gas, which doesn'teither dissolve or generate byproducts by itself, into a reactionchamber where substrates are placed introducing the purge gas into theinside of the reactive gas confining means having plural openings; andsupplying a source material of vapor phase participating directly informing a film on the substrates to an inside of the reaction chamber,thus forming a protective curtain in the inside of the reaction chamberby a mutual diffusion-suppressing action between the purge gas andsource material. According to the method for CVD of the inventiondescribed above, it is possible to increase the density of sourcematerial substantially only in the vicinity of the substrates andenhance film growth rate remarkably.

It is a further object of the present invention to provide a method forCVD comprising steps of: establishing a reactive gas confining means,having a plurality of openings, in a reaction chamber; injecting a purgegas, which doesn't either dissolve or generate byproducts by itself,into an outside of the reactive gas confining means; and supplying asource material of vapor phase participating directly in forming a filmto an inside of the reactive gas confining means, thus dividing aninside of the reaction chamber into a first region where a density ofthe source material is high and a second region where the density of thesource material is extremely low.

Another object of the present invention is to provide the method for CVDdescribed above, wherein the reactive gas confining means has aplurality of openings through which the purge is introduced to theinside of the reactive gas confining means, thus preventing the sourcematerial from diffusing to the outside of the reactive gas confiningmeans, and forming a protective curtain that prevents the sourcematerial from touching the reactive gas confining means.

An additional object of the present invention is to provide the methodfor CVD described above, wherein an amount of the purge gas injected tothe outside of the reactive gas confining means is set much larger thanthat of the source material supplied to the inside of the reactive gasconfining means to direct the protective curtain of purge gas from theoutside to the inside of the reactive gas confining means, thuspreventing the source material from touching the reactive gas confiningmeans.

Yet another object of the present invention is to provide an apparatusfor CVD, including a susceptor located in a reaction chamber producing avacuum, on which substrates are placed and a film deposition process ismade, the apparatus comprising: a reactive gas confining means,established over the susceptor, having at least a source material supplyport through which a source material is supplied and a plurality ofopenings perforated on a surface thereof; a purge gas supply portthrough which a purge gas is fed into an outside of the reactive gasconfining means; and an exhaust port for discharging exhaust gassesgenerated in the reaction chamber.

Still another object of the present invention is to provide an apparatusfor CVD including a boat, established in a reaction chamber in ahorizontal direction, on which a plurality of wafers are placed, theapparatus comprising: a reactive gas confining means, provided in ahorizontal direction to envelop the boat, having a plurality of openingsperforated on a surface thereof, a source material supply means on oneend thereof and an exhaust port for discharging byproducts on the otherend thereof, thus forming a protective curtain in an inside of thereaction chamber by a mutual diffusion-suppressing action between apurge gas injected to an outside of the reactive gas confining means anda source material supplied to an inside of the reactive gas confiningmeans.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention:

In the drawings:

FIGS. 1, 2 and 3 are schematic views showing various types ofconventional CVD apparatus;

FIG. 4 is a conceptional view showing a reaction chamber where areactive gas for depositing films is filled up;

FIG. 5 is a conceptional view showing a reaction chamber where a purgegas is filled up;

FIG. 6 is a conceptional view depicting the status that the reactive gasis confined in the midst of the chamber where a purge gas is filled up;

FIG. 7 is a partially cut perspective view illustrating a basic conceptof a reaction chamber of a CVD apparatus in accordance with a preferredembodiment of the present invention;

FIG. 8 is a perspective view showing an example of a reactive gasconfining means in accordance with the invention;

FIGS. 9A, 9B and 9C shows various types of reactive gas supply portformed on the top of the reactive gas confining means in accordance withthe invention;

FIG. 10 shows a swirl phenomenon of the reactive gas injected throughthe inclined reactive gas supply ports depicted in FIG. 8C in accordancewith another embodiment of the invention;

FIGS. 11 and 12 depict another examples of the reactive gas confiningmeans in accordance with the invention;

FIGS. 13, 14, 15 and 16 are schematic sectional views showing varioustypes of the reaction chamber where the reactive gas confining means isprovided in accordance with the present invention;

FIG. 17 is a graph showing variations of Tio₂ growth rate based on theheights of the susceptor in the reaction chamber in accordance with theinvention;

FIG. 18 shows a drift velocity vector of a mixed gas composed of thereactive gas and the purge gas in the CVD apparatus in accordance withthe invention;

FIG. 19 shows how the density of the reactive gas is distributed in theCVD apparatus in accordance with the invention;

FIG. 20 is a graph illustrating variations of TiO₂ growth rate based onthe purge gas flow rates in accordance with the invention;

FIG. 21 is a graph depicting variations of TiO₂ growth rate obtained byusing a conventional showerhead type CVD apparatus and the CVD apparatusof the present invention;

FIGS. 22 and 23 show variations of TiO₂ growth rate based on the vacuumpressures in the reaction chamber in accordance with the invention

FIG. 24 illustrates variations of TiO₂ growth rate based on the TIP flowrates in accordance with the invention;

FIG. 25 is a cross-sectional electron microscope view of a TiO₂ filmformed on a bare silicon wafer in accordance with the invention;

FIG. 26 is a cross-sectional electron microscope view of aPZT/Ni/TiO₂+ZrO₂ film on a Si₃N₄ layer in accordance with the invention;

FIG. 27 is a cross-sectional electron microscope view of a PZT filmgrown on a bare silicon wafer in accordance with the invention; and

FIG. 28 is a graph showing variations of TiO₂ growth rate based on theheights of the susceptor in the reaction chamber according to anotherembodiment of the reactive gas confining means depicted in FIG. 7 of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Referring to FIGS. 4 to 6, there are provided a purge gas supply port 27through which a purge gas is fed into a reaction chamber 3, a reactivegas supply port 7 through which a reactive gas is supplied into thechamber 3, a susceptor 5 for supporting and heating the substrate and anexhaust port 28 for discharging byproducts in the chamber 3. When apredetermined reactive gas is injected into the chamber 3 of lowpressure, the reactive gas is diffused instantly in all directions;likewise, the purge gas fed into the chamber 3 is diffused instantly inall direction. However, as depicted in FIG. 6, when the reactive gas issupplied into the midst of the chamber 3 where the purge gas is filledup, there is formed a protective curtain B between the reactive gas andpurge gas filled up due to a mutual diffusion-suppressing action, thusdividing the interior space of the chamber 3 into two portions A and C.

The purge gas doesn't either dissolve or generate byproducts by itselfin the chamber 3. For example, the purge gas includes Ar, He, H₂, N₂etc. as a carrier gas, Ar, N₂ as a dilution gas, and O₂ which doesn'tgenerate byproducts by itself. The purge gas of small molecular weight,which diffuses instantly, is relatively little influenced by the act ofvacuum pumping.

Meanwhile, the reactive gas is a source material of vapor phase thatparticipates directly in forming the film; a mixture of vapor phasecontaining a main source material and an auxiliary source material forcarrying, vaporizing or diluting the main source material; or a puremain source material of vapor phase without carrier gas for carrying themain source material. In this regard, the Korean Patent No. 225592teaches a method for vaporizing and delivering such reactive gas withoutthe aid of carrier gas in a metal-organic chemical vapor depositionprocess (MOCVD).

According to the present invention, when the purge gas and the reactivegas are supplied separately into the reaction chamber 3, the reactivegas is highly concentrated at a region proximate to the susceptor 5located in the midst of the chamber 3 (portion A), whereas the purge gasgathers in the vicinity of the inner wall of the chamber 3 (portion C).That is, when the reactive gas is fed into the midst of the chamber 3where the purge gas is filled up in advance, there is formed aprotective curtain B, which divides the interior space of the chamber 3into two portions A and C, having different density distributions witheach other. Accordingly, it is possible to increase the film growth ratewith the increase of the reactive gas density, and to prevent generationof contaminant particles on the inner wall of the chamber 3, since thereactive gas doesn't exist over the inner wall of the chamber 3.However, a minute temperature difference between the inner wall of thechamber 3 and the susceptor 5 may cause a natural convection, whichmakes it very difficult to maintain the protective curtain B stably.That is, the protective curtain B is ready to get broken by the naturalconvection or variations of the amount of the two gasses supplied.Consequently, it is hard to adopt the method using the unstableprotective curtain B to the chemical vapor deposition that needsprecision, uniformity and high growth rate.

To overcome the problem described above, the present invention providesa reactive gas confining means 1 as an auxiliary means for keeping theprotective curtain B stably. As depicted in FIG. 7, the reactive gasconfining means 1 is established in the midst of the chamber 3. Themeans 1 has a proper volume and type capable of surrounding theprotective curtain B therein. Reactive gas supply ports 7 are providedon the top of the means 1, a showerhead 9 through which the purge gaspasses into the chamber 3 is established over the means 1, and asusceptor 5 on which substrates are placed is provided within the means1. Besides, an exhaust port 18 for discharging byproducts is locatedbetween the susceptor 5 and the means 1.

The reactive gas confining means 1, established a little bit outsidebased on the protective curtain to be formed desirably between the purgegas and the reactive gas, prevents the protective curtain from beingbroken by complementing the mutual diffusion-suppressing action betweenthe two gasses, thus protecting and keeping the protective curtainstably. That is, when the purge gas is fed into the chamber 3 through apurge gas supply port, not depicted, the purge gas is readily diffusedto the inside of the means 1 through a plurality of openings 13perforated on the surface of the means 1. Next, when the reactive gas issupplied to the inside of the means 1 through the reactive supply ports7, the reactive gas concentrated within the means 1 presses the purgegas outwardly, thus forming a predetermined protective curtain.Contrarily, a portion of the purge gas is forced to diffuse to theinside of the means 1 through the openings 13, thus strengthening theprotective curtain to be kept stably, regardless of the naturalconvection or variations of the purge gas flow.

Hereinafter, various embodiments of the reactive gas confining means 1in accordance with the invention will be described in detail. The means1, depicted in FIG. 8, is designed most similar to the shape of theprotective curtain formed between the purge gas and the reactive gas,and to envelop the susceptor 5 thoroughly. That is, the means 1comprising a mixing part 21, a diffusion part 23 and a deposition part25 in a body flattens the density contour of the reactive gas inparallel to the upper side of the substrates, thus depositing filmsuniformly in thickness. The means 1 is made of heat and corrosionresistant materials such as stainless steel, ceramic, quartz, orreinforced glass by various methods such as spinning, casting, ormolding based on the materials used. The openings 13 are madeappropriately by drilling, casting or molding based on the materialsused. The size and interval of the openings 13 are designed properly tomake a protective curtain, a unique effect of the reactive gas confiningmeans 1. Here, the protective curtain forces the reactive gas fed to theinside of the means 1 not to diffuse outwardly. The size and interval ofthe openings 13 are suitably regulated to 3 mm in diameter and atintervals of 20 mm, for example, however, not limited since they can bevaried according to various factors such as flow rates of the twogasses, density of the reactive gas and overall size of the apparatusused.

Meanwhile, returning to FIG. 7, the showerhead 9 has a plurality ofperforations 19 for supporting the protective curtain, of which theintervals can be varied also. For example, the intervals of theperforations 19 in the midst of the showerhead 9 are set wide, whereas,those around the edge of the showerhead 9 are narrow, thus creating adifference in density of the reactive gas within the reaction chamber 3.As a result, the purge gas flow is directed toward the inside of thereactive gas confining means 1. Actually, however, in case that themeans 1 is installed in the chamber 3, the same effect can be obtainedalso by the mere work of the purge gas supply port 27, depicted in FIG.6, instead of the showerhead 9.

Repeatedly, referring to FIG. 8, the mixing part 21 having a relativelysmall diameter mixes the main source material and the auxiliary sourcematerial rapidly in the narrow space thereof. Besides, the purge gasdiffused through the openings 13 formed around the surface of the mixingpart 21 helps the source materials to be mixed in the midst of themixing part 21, while preventing generation of contaminant particles onthe inner wall of the mixing part 21.

The reactive gas supply ports 7 established on the top of the mixingpart 21 can be configured to have various types. For example, a singleperpendicular conduit as a reactive gas supply port 7, shown in FIG. 9A,can be adopted when the main and auxiliary source materials mixed inadvance or a pure main source material of vapor phase without carriergas is injected. Besides, as shown in FIGS. 9B and 9C, a plurality ofperpendicular or inclined conduits, as another types of the reactive gassupply port 7, can be used when various kinds of the source material,mixed or unmixed, are injected directly. Here, the source materialinjected through the inclined ports 7 of FIG. 9C induces a swirlphenomenon (an effect of cyclone), which lengthens traveling path of thesource materials supplied, thus mixing the source materialssatisfactorily. Accordingly, when it is required to establish a longpath through which the source materials travel, or when the axial lengthof the reaction chamber 3 is short, it is desired to feed the reactivegas into the chamber 3 in the inclined direction, as shown in FIG. 9C.The reactive gas supply port 7 having an internal diameter less than 10mm is formed with a tubular tube made of stainless steel, ceramic,Teflon, etc. The reactive gas supply port 7 is connected to bubbler,vaporizer, etc., not depicted, to supply the reactive gas to the insideof the means 1.

The diffusion part 23, of which diameter becomes wider downward,diffuses high concentrated reactive gas mixed in the mixing part 21 inan inclined direction, thus flattening the density contour. Afterwards,the high density of the reactive gas gets decreased while it is diffusedin the inclined direction through the diffusion part 23 that growsvoluminous downward. Here, the diverging angle and the height of thediffusion part 23 are closely related with the flow rate of the reactivegas. For example, if the diffusion process occurs rapidly, the divergingangle of the diffusion part 23 may get increased and the height belowered.

The longitudinal deposition part 25 is a region where the flatteneddensity contour of the reactive gas meets parallel to an upper side 15of the susceptor 5. The upper side 15 of the susceptor 5, on which filmis formed substantially, should be located to a region where the densityof the reactive gas is set adequate and the density contour issufficiently flattened. Accordingly, the longitudinal deposition part 25is designed to have an ample height enough to surround the upper side 15of the susceptor 5. Besides, to discharge exhaust gas smoothly, it isalso desired to increase the height of the deposition part 25 as much aspossible. The plural openings 13 perforated on the surface of the means1 are configured to induce a portion of the purge gas distributed to theoutside of the reactive gas confining means 1 to diffuse in a normaldirection to the surface of the means 1. As a result, the reactive gasis impeded to escape outside from the means 1 by means of the protectivecurtain of purge gas. Besides, the highly concentrated reactive gas aptto diffuse outward also prevents the purge gas from permeating to theinside of the means 1 over a predetermined depth. Accordingly, there isformed a protective curtain in the inside of the reaction chamber 3 dueto the mutual diffusion-suppressing action between the two gasses. As aresult, it is possible to confine the reactive gas to the inside of themeans 1, without touching the inner wall of the means 1, by regulatingthe amounts and flow rates of the two gasses properly. Consequently, inthe CVD apparatus in accordance with the present invention, there arenot generated contaminant particles on the inner wall of the chamber 3and the inner and outer walls of the means 1 as well.

Meanwhile, the reactive gas confining means 1 according to the inventionis not limited to the form depicted in FIGS. 7 and 8, but can bedesigned to various forms based on the characteristics of the reactivegas and the conditions of the chamber 3. For example, the means 1 shownin FIG. 11 has no mixing part 21, and the diverging angle of thediffusion part 23 thereof is increased sharply. This type of the means 1can be adopted when the diffusion rate of the reactive gas is very high,and advantageously employed when using a large size substrate. The othercomponents of the means 1 of FIG. 11 have the same functions with thatof FIG. 8. The means 1 depicted in FIG. 12 includes no diffusion part 23as well as the mixing part 21, but only the deposition part 25 having apredetermined height. In this case, the protective curtain can be formedthrough the openings 13 in the same manner described above, however, thereactive gas fed to the inside of the means 1 doesn't diffuse readily,thus deteriorating the horizontal uniformity of the reactive gasdensity.

Accordingly, it is desired to establish the reactive gas supply port(s)7 as shown in FIGS. 13 and 14. The reactive gas supply ports 7 in FIG.13 penetrate the means 1 through a plurality of reactive gas supplypaths 37 provided on the top of the means 1 at regular intervals tosupply the reactive gas to the inside of the means 1 uniformly.Meanwhile, the reactive gas supply port 7 in FIG. 14 is connected with ashowerhead 29 in the means 1 to spread the reactive gas wide anduniformly.

With reference to FIG. 15, there is shown another type of the reactivegas confining means 1 in accordance with the present invention having adome-like shape of low height, which excludes the mixing part, diffusionpart and deposition part. That is, when the reactive gas and purge gasare fed separately into the midst of the reaction chamber 3 where thepurge gas is filled up, there is formed a protective curtain over thesusceptor 5. Here, the dome-like reactive gas confining means 1 preventsthe protective curtain from being broken. Besides, if the showerhead 9is further provided over the means 1, it is much helpful to create amore stable protective curtain.

Next, referring to FIG. 16, the reactive gas confining means 1 inaccordance with the present invention is applied to a low-pressurechemical vapor deposition (LPCVD), where a plurality of wafers 47 standserect on a boat 45 established in a horizontal direction. Here, thecylindrical means 1 provided in the same direction with the boat 45 hasa plurality of openings 13 perforated on the surface thereof, a reactiongas supply port 7 on one end thereof extended to a side wall of areaction chamber 3 mainly comprising a mixing chamber 49, and an exhaustport 48 for discharging byproducts on the other end thereof. When thepurge gas is fed into the outside of the means 1 and the reactive gas issupplied to the inside of the means 1, the purge gas is introduced tothe inside of the means 1 through the openings, thus creating theprotective curtain between the purge gas and reactive gas in the means1. Accordingly, the density of the reactive gas concentrated around theboat 45 on which the plural wafers 47 are placed is increased. However,there exists no reactive gas on the inner wall the reaction chamber 3,and the inner and outer surfaces of the means 1 as well, thus preventinggeneration of contaminant particles.

That is, according to the CVD apparatus using the reactive gas confiningmeans 1 and the protective curtain of purge gas of the presentinvention, the density of the reactive gas concentrated in the midst ofthe reaction chamber 3 is increased more than several or several tens oftimes compared with that in the other region by supplying the purge gasinto the outside of the means 1 while feeding the reactive gas to theinside of the means 1, separately.

In addition to this, neither the local re-circulation caused by theinconsistency of chamber geometry nor the natural convection caused bytemperature difference between the relatively cold wall of the chamber 3and the hot susceptor 5 seems to occur easily inside the means 1, sincethe purge gas flow has a direction normal to the surface of the means 1and exerts a stabilizing effect as followings. The purge gas which wasdirected from the outside to the inside of the means 1 confines thereactive gas into the means 1 and makes laminar flowing state of thereactive gas in the vicinity of the substrate. This effect can beregulated by the purge gas flow rate that would be, for example, severaltimes as large as the reactive gas flow rate.

Consequently, the present invention is disclosed to increase the filmgrowth rate and the uniformity of the film thickness remarkably, andminimize the generation of the contaminant particles by designing thegeometry of the reaction chamber 3 optimally including the type ofreactive gas confining means 1, the location of susceptor, etc., and bycontrolling the amount of purge gas flow, and the mixing, diffusion andexhaust of source materials properly.

Hereinafter, various embodiments of the method and apparatus for CVDcapable of preventing contamination and enhancing film growth rateaccording to the present invention will be described in followingexamples.

EXAMPLE 1 Configuration of CVD Apparatus

In a preferred embodiment in accordance with the present invention, asshown in FIG. 7, the reactive gas confining means 1 having a diameter of300 mm and a height of 445 mm was provided to surround the susceptor 5,having a diameter of 240 mm and a height of 80 mm, positioned in themidst of the reaction chamber 3. The means 1 employed has a funnel-likeshape through which the purge gas is diffused to the inside of the means1. The reactive gas supply ports 7 were equipped on the top of the means1 and the purge gas supply port 9 provided over the means 1.

EXAMPLE 2 TiO₂ Film Deposition

TiO₂ film deposition was made using the CVD apparatus described inExample 1. Following equation denotes TiO₂ film deposition by TIPpyrolysis.Ti(OC₃H₇)₄→TiO₂(s)+4C₃H₆+2H₂O

Titanium iso-propoxide (TIP, Ti(OC₃H₇)₄) was employed as a precursor forTiO₂ film deposition. The vapor pressure of TIP was 2 Torr at 70° C. Theheating temperature of TIP was 85° C., and the reaction chamber pressurewas 133 Pa. Pure TIP gas was supplied to the inside of the means 1 at aflow rate of 1×10⁻⁶ kg/sec without the aid of carrier gas, whereas Argonas purge gas was injected into the outside of the means 1 at a flow rateof 10×10⁻⁶ kg/sec. At appropriately low heating temperatures, i.e., atthe range from 70° C. to 100° C., TIP can be easily vaporized but hardlydecomposed in the TIP container. Pure vapor of TIP can be deliveredwithout the aid of carrier gas into the chamber 3 where the chamberpressure is much lower than the TIP vapor pressure. Here, there is anadvantage that facilitates quantitative analysis of the metal organiccompounds used in the MOCVD process. To simulate the depositionbehavior, a computational fluid dynamics program, Fluent, was utilized.Herein, Lennard Jones parameter was introduced for convenience since thekinetic theory can easily calculate the theoretical physical propertiesof TIP such as diffusion coefficient, thermal conductivity, specificheat etc. L-J characteristic length (Angstrom) and energy parameter (K),which are the values of Lennard Jones parameters of TIP and other gases,can be referenced elsewhere.

EXAMPLE 3

As shown in FIG. 17, TiO₂ film deposition was made at various heights ofthe susceptor from the bottom of the means 1 with the CVD apparatus andconditions described in Examples 1 and 2, respectively, while keepingthe uniformity of the deposition within ±5% in the range less than 100mm in radial position. It was understood that the reason why the filmgrowth rate beyond the radial position 100 mm, i.e., the edge portion ofthe upper surface of the susceptor, is increased steeply is because thevelocity vector is abruptly changed in this vicinity.

EXAMPLE 4

FIG. 18 depicts the drift velocity vector of the mixed gas composed ofthe reactive gas and purge gas. The maximum velocity was about 1.5m/sec. it can be seen that there was formed the protective curtain thatconfines the highly concentrated reactive gas in the midst of thereaction chamber 3 from the outside to inside of the means 1. Besides,FIG. 19 illustrates how the density (mass fraction) of the TIP isdistributed in the CVD apparatus in accordance with the invention. Themaximum and minimum concentrations are 100% and 0%, respectively, andthe contour is drawn at the interval of 1%. It can be noted that thepurge gas fed to the inside of the means 1 doesn't so much decrease thedensity of the TIP injected from the reactive gas supply ports 7 at themixing part 21. Moreover, due to the effect of the protective curtainhaving a normal direction from the outside to the inside of the means 1,the density of the TIP adjacent to the inner wall of the chamber 3 isdetected extremely low, such that there were not generated unwantedcontaminant particles on the inner wall of the chamber 3. In addition tothis, the net velocity of the TIP, i.e., the vector sum of the driftvelocity of the mixed gas and the TIP diffusion velocity, can beselected to have a normal direction from the outside to the inside ofthe means 1. That is, since the range of the purge gas flow rate to beselected is very wide, for example, several to several tens times aslarge as the TIP flow rate, while keeping the uniformity of the TiO₂growth within +5% in practice, there is no possibility that the netvelocity of the TIP exists eventually in the direction from the insideto the outside of the means 1.

EXAMPLE 5

FIG. 20 shows variations of Tio₂ growth rate based on the purge gas flowrates, obtained when supplying the pure TIP vapor not diluted to theinside of the means 1 of the CVD apparatus described in Example 1. Itwas noted that the protective curtain, which confines the TIP flowwithin the means 1, becomes thicker accordingly as the purge gas flow isincreased. That is, at the purge gas flow rate of 20×10⁻⁶ kg/sec, theTiO₂ growth rate was the highest and relatively uniform in the radialdirection of the susceptor. However, if the purge gas flow rate is morethan 300×10⁻⁶ kg/sec, the TIP vapor may be over-concentrated in themidst of the chamber 3. As a result, the TiO₂ growth rate in the midstof the 200 mm Si wafer on the substrate, for example, was much higherthan that in the edge portion of the wafer.

EXAMPLE 6

Next, FIG. 21 depicts variations of TiO₂ growth rate obtained by using aconventional showerhead type CVD apparatus and the CVD apparatusdescribed in Example 1. Here, input mass fraction of TIP is defined asthe ratio of TIP input mass flow rate to total input mass flow rate. Itwas found that at all input mass fractions of TIP, the present invention(▪●♦) provides much higher TiO₂ growth rate than that of conventionalmethod (□◯⋄). For example, if the input mass fraction of TIP is 10%, theTiO₂ growth rate of the present invention (●) is more than 30% higherthan that of the conventional, method (◯). If the input mass fraction ofTIP is 1%, the TiO₂ growth rate of the present invention (♦) is morethan 300% higher than that of the conventional method (⋄).

EXAMPLE 7

As depicted in FIGS. 22 and 23, showing variations of TiO₂ growth ratebased on vacuum pressures in the chamber 3, it was found that the TiO₂growth rate gradually increases accordingly as the chamber pressurerises, and reaches a maximum value at a pressure of 133 Pa, then slowlydecreases at pressures more than 133 Pa. Besides, it was noted that theTiO₂ film growth rate is not sensitively influenced by the chamberpressure within a wide range around 133 Pa, which allows plenty of scopefor the change of vacuum pressure in mass production.

EXAMPLE 8

As shown in FIG. 24, illustrating variations of TiO₂ growth rate basedon the TIP flow rates, it was noted that the growth rate of TiO₂ filmincreases remarkably according as the flow rate of TIP rises when usingthe means 1 of the invention. Especially, when delivering the pure TIPvapor without carrier gas to the inside of the means 1, TiO₂ film growthrate increased in proportion as the input flow rate of TIP rose. Thatis, since it is very easy to increase the input flow rate of TIP whensupplying the pure TIP vapor without carrier gas, it is desired toemploy the pure TIP vapor without carrier gas when it is necessary toensure high growth rates.

EXAMPLE 9

FIG. 25 is a cross-sectional electron microscope view of a TiO₂ filmformed on a bare silicon wafer using the CVD apparatus accordance withthe invention. The TiO₂ film was formed 8 μm in thickness at a growthrate of 20 μm/h in the chamber 3 at a pressure of 133 Pa. It can beunderstood that the growth rate obtained in this example is remarkablyhigh, which shows a superiority of the present invention for depositingthick films.

Meanwhile, FIG. 26 is a cross-sectional electron microscope view of aPZT/Ni/TiO₂+ZrO₂ film on a Si₃N₄ layer using the CVD apparatus inaccordance with the invention. At first, TiO₂+ZrO₂ layer was depositedon a nitride silicon wafer, where TIP and Zirconium tert-butoxide wereprecursors for TiO₂ and ZrO₂ components, respectively. Then, Nielectrode was formed on the TiO₂+ZrO₂ layer by RF sputtering. FinallyPZT layer was deposited using the present invention. Here,tetraethyl-lead (Pb(C₂H₅)₄) was adopted as a precursor for a leadcomponent together with TIP and Zirconium tert-butoxide described above,and oxygen was used to make lead oxide compounds which also constitutePZT. As shown in FIG. 26, the film thickness of TiO₂+ZrO₂ grown on theSi₃N₄ layer is about 5 μm and the film thickness of PZT film formed on aNi electrode is about 3 μm.

EXAMPLE 10

Next, FIG. 27 is a cross-sectional electron microscope view of a PZTfilm grown on a bare silicon wafer using the CVD apparatus in accordancewith the invention. The PZT film was formed 6 μm in thickness at agrowth rate of 6 μm/h in the chamber 3 at a pressure of 200 Pa. It canbe recognized that the morphology of the deposited PZT film is not soplanar, but the thickness of the PZT film obtained according to thepresent invention is much enhanced compared with the conventionalmethods described earlier, and may belong to the thickest one among thePZT films prepared by the metal-organic chemical vapor deposition(MOCVD).

EXAMPLE 11

Finally, FIG. 28 is a graph showing variations of TiO₂ growth rate basedon the heights of the susceptor in the chamber 3 according to anotherembodiment of the means 1 having no mixing part depicted in FIG. 11. Inthis embodiment, the full height of the means is 300 mm and the otherconditions are the same with that of Example 1. As shown in FIG. 28, itwas noted that the film growth rates increases outstandingly, whereas,the uniformity of the film growth deteriorates more or less. That is, itteaches that, for securing the uniformity of the film growth, it isnecessary to flatten the density contour of the source materials byincreasing the length of the means 1 sufficiently. Accordingly, theaxial length of the means 1 should be determined circumspectly in termsof both the structural efficiency and the uniformity of the film growth.

According to the present invention described above, it is possible toincrease the density of the reactive gas using the effect of protectivecurtain caused by introducing the purge gas to the inside of the means 1for confining the reactive gas in the midst of the reaction chamber 3where the film growth is made, thus enhancing the film growth rateremarkably.

Besides, according to the effect of protective curtain of the invention,it is possible to prevent generation of contaminant particles on theinner wall of the reaction chamber 3.

Furthermore, according to another embodiment of the invention, there isprovided a reactive gas confining means 1, of an appropriate size andshape that can surround the susceptor 5 in the reaction chamber 3,having the plural openings 13, perforated on the surface thereof,through which the purge gas is introduced. With the means 1, it ispossible to prevent generation of contaminant particles on the surfaceof the means 1 using the effect of the protective curtain caused by themutual diffusion-suppressing action between the reactive gas and purgegas by regulating the purge gas flow and the diffusion rate so as tointroduce the purge gas, fed to the outside of the means 1, to theinside of the means 1.

Moreover, according to the reactive gas confining means 1 of theinvention, it is possible to mix and diffuse the reactive gas rapidlyand smoothly, and to prevent the natural convection caused by atemperature difference between the components in the reaction chamberthus enhancing the reproducibility, uniformity, controllability, andgrowth rate remarkably.

In addition, according to the invention, it is possible to increasenoticeably the concentration of the reactive gas in the midst of thereaction chamber 3 where the film growth is made, without any losses ofthe reactive gas, compared with the conventional CVD apparatus, and toprevent generation of contaminant particles, which may be caused by thehighly concentrated reactive gas, thus efficiently forming thick filmsmore than 3 μm in thickness applied to the micro-electro mechanicalsystem (MEMS), etc.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method and apparatus forCVD capable of preventing contamination and enhancing film growth rateof the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. An apparatus for CVD including a vertical type reaction chambercomposed of a vertical wall, a ceiling, a bottom, and a susceptorlocated over the bottom of the reaction chamber, on which substrates areplaced and a film deposition process is made as a result of chemicalreactions with supplied source materials, the apparatus furthercomprising: a reactive gas confining means for surrounding thesusceptor, disposed in the reaction chamber, composed of a vertical walland a ceiling, having a plurality of openings perforated on a surfacethereof for communication of inside with outside of the reactive gasconfining means, wherein the vertical wall and the ceiling of thereactive gas confining means are respectively separated from those ofthe reaction chamber at a distance, and the vertical wall is extended tothe bottom of the reaction chamber such that a space having apre-determined thickness is formed between the ceilings of the reactionchamber and the reactive gas confining means; a plurality of ports forsupplying source materials into the reactive gas confining means, formedon the ceiling of the reactive gas confining means, coupled to tubularconduits in communication with the ceiling of the reaction chamber suchthat the tubular conduits supply the source materials in the reactionchamber through the space and into the reactive gas confining means; apurge gas supply port for supplying a purge gas formed on the ceiling ofthe reaction chamber; and an exhaust port located at the inside of thereactive gas confining means for discharging exhaust gasses generated inthe reaction chamber wherein the purge gas injected from the port formedon the ceiling of the reaction chamber flows through the space and intothe reactive gas confining means via said plurality of perforatedopenings, whereby the flow rate of the purge gas into the reactive gasconfining means is positively regulated so as to prevent contaminationof the reactive gas confining means and to enhance a film growth rate onthe substrates by increasing the concentration of the source materialsin the vicinity of the substrates.